1. Field of the Invention
The invention relater to a raised emitter of a gas heating appliance for infrared and luminous radiation for directional heating, capable of supplying at very low pressures of gas supply a raised radiation output. This emitter is intended for heating appliances for surfaces in industrial locations, craft. agriculture and service locations and for every use in the open air or partly in the open air.
2. Description of the Related Art
In the current state of the art, heating appliances which have an emitter of infrared radiation are used now, certain of which have a very good radiation output such as that described in document EP 0 382 286 in the name of the applicant. Nevertheless, obtaining this high output is conditioned by a nominal pressure of gas supply substantially greater than that provided for the emitter which is the object of the invention.
Other appliances have a good output at a low pressure of gas supply, These are classic radiants with perforated plates formed from refractory ceramics. These plates are crossed by the air-gas mixture entering via one face, bursting into flame and radiating on the other face. The limiting factor of the use of these appliances with ceramic plates it their lack of adaptation to dusty environments because cleaning them is difficult and washing them in water is not compatible with ceramic plates, The disadvantage of these plates is also their fragility and every cracked plate must be changed for fear of communicating the flame to the internal face of this plate. Poor resistance to airflows must also be added.
Finally there also exist appliances which are entirely metallic and function according to the same scheme as the appliances with ceramic plates, the latter being replaced by a sheet of thin and finely perforated metallic netting. The position of this netting should deviate very little from the horizontal especially because of the fact that if the appliance is inclined, the air-gas flow arriving from the top to the bottom, on the internal side, in the middle of the sheet of netting, the lower half of the netting does not receive, on the internal side, any more than a tiny portion of the fuel-oxidiser mixture and the combustion on the external side becomes insignificant over all this lower halt which does not redden. By contrast, the top half receiving twice its requirement of the mixture of fuel-oxidiser, abnormal overheating is noted. Now the interest of a downwardly directional infrared emitter is not to be limited to a restricted zone close to the vertical, but to be able to provide oblique radiation of greater amplitude in the desired directions.
To attempt to reduce this disadvantage of a netting which is too hot over one half and too dark over the other, there is certainly provided, on the internal side, a netting with a larger mesh, parallel to the radiation netting, to spread out the flow. If the result is partially achieved when one departs no more than a few degrees from the horizontal position, the effect is practically zero on the radiation netting in the oblique position.
Finally the fact that there is only provided on this type of emitter a single finely perforated netting for a radiation surface corresponding to the nominal value of the power of the appliance. makes this type of appliance scarcely prone to bearing a temperature level corresponding to a very interesting portion of the infrared wavelengths with good radiation output. Experience shows that a single metallic netting, heated to more than 700xc2x0 C. and receiving an air-gas flow at low speed (as a result of the low pressure), is not capable of combating effectively the risk of catching fire internally.
Finally for all the appliances mentioned above, the resistance to airflows is a factor which limits in practice their use to an air speed of the order of 1 meter/second at the maximum.
The present invention also intends to overcome the disadvantages of these heating appliances with infrared emitters and in particular when it is required to use a very low pressure as a nominal value, lower than 50 mbar.
Another objective of the invention is to obtain on perforated refractory walls which are inoxidizable and non-porous, oblique or vertical:
perfectly distributed radiation;
high-temperature infrared emission to enjoy a raised radiation output, i.e. a high percentage of radiated heat in relation to the total heat produced.
The objective should then be, to ensure great reliability in functioning at high temperature, to combine adequate conditions for the temperature to be as high as possible at the external surface of the emitter whilst being more moderate in the interior, but nevertheless sufficient to ensure the pyrolysis of organic dusts.
Another objective of the invention is to permit, via the inoxidizable and non-porous nature of the emitter, washing in water, both internally and externally.
Finally, as will be shown further on, the design of the structure of the invention makes it possible to achieve two supplementary objectives;
silent functioning,
a great resistance to wind.
The infrared emitter according to the invention is thus suitable for numerous applications when the available gas source can or should be delivered only at a very low pressure, whether these be constraints specific to certain distribution networks, constraints imposed by respecting regulations or even constraints of partial replacement of existing appliances, in complete installations designed for very low pressures, i.e. for pressures generally of between 15 and 50 mbar. These applications relate to numerous fields in which a raised heating device operating with a directional infrared emitter is at the same time the most widespread and the most economic solution in agriculture, industry, the service sector and other sectors.
More precisely, the invention consists in an infrared emitter with luminous radiation for a supply of gas at very low pressure and of primary atmospheric air via venturi, said supply comprising at least one gas injector, an injector holder, a safety valve, a gas supply connector, especially for raised heating appliances for directional heating towards the ground and/or on the sides in the agricultural, industrial, craft and service sectors, characterized in that it comprises:
a geometrical structure comprising at least one first, second, third and fourth concentric enclosures,
a substantially horizontal upper plate below which the said at least first, second, third, fourth enclosures are fixed concentric with said plate, the one fitting inside the other,
a central opening leading the air-gas flow perpendicularly to said plate, into the interior space created by the first enclosure.
According to another feature, the emitter according to the invention comprises a fifth enclosure which is also concentric and which can be inserted between the second and third enclosures according to the gas supply pressure conditions and the instability of the ambient air of the environment.
According to another feature, the emitter according to the invention comprises a first, second, third and fourth enclosure, the second enclosure then fulfilling the functions equivalent to those ensured by the conjunction of the second and fifth enclosures of the emitter, according to the above features, all these enclosures having on a surface of revolution over 360xc2x0, lateral, oblique, vertical or hemispherical walls formed from an inoxidizable refractory material which is permeable and non-porous and which turns red with heat.
According to another feature, the emitter according to the invention comprises a supply of the air-gas flow directed from the top to the bottom, and an integral central opening in said plate, then open in its centre, airtight with the plate, leading the air-gas flow perpendicularly to said plate via the central opening of the latter into the interior space created by the first enclosure.
According to another feature, the emitter according to the invention comprises a supply of the air-gas flow directed from the bottom to the top and a central opening contiguous with the second and third enclosures and loading the air-gas flow perpendicularly to the upper plate, then full in its centre, into the interior space created by the first enclosure.
According to another feature, the lateral walls of the second, fifth and third enclosures are kept spaced by spacing means such as raised ribs formed on these enclosures, keeping them at a controlled distance the one from the other and serving them as strengtheners against heat deformation without obscuring the luminous emission at the contact lines of the reliefs, this spacing distance being moreover limited to the passage of a thin layer of dynamic flow making its way through the holes of the specific perforated walls firstly of the second and fifth enclosures, and secondly of the fifth and third enclosures.
According to another feature, the distribution enclosure in its truncated-cone, cylindrical or hemispherical shape, comprises in its internal volume, according to the central vertical axis of symmetry, a solid or very finely perforated cone, apex towards the top at the outlet for the arrival of the air-gas flow, thus giving in combination with the first enclosure in the above shapes an equivalent means of perfect distribution of the air-gas flow to that obtained directly with the first enclosure, apex towards the bottom of the conical shape.
According to another feature, the distribution enclosure for the truncated-cone, cylindrical or hemispherical shapes, comprises in its internal volume, according to the central vertical axis of symmetry, a solid cone of pre-distribution, base towards the plate and apex towards the bottom at the outlet for the arrival of the air-gas flow, thus becoming in combination with the first enclosure in the above shapes a means of perfect distribution of the air-gas flow.